The present invention relates to a composition made from cycloolefin copolymers (COCs) and from additives for improving stress cracking resistance. The polymer composition of the invention has improved resistance to stress cracking in air, and also in contact with media which give rise to stress cracking.
The lack of resistance of various plastics to stress cracking in air, and also in contact with media which give rise to stress cracking, is a serious problem, since it severely restricts the usefulness of the plastics and reduces the lifetime of the associated components.
Surprisingly, it has been found that a polymer composition which comprises one or more cycloolefin copolymers and one or more suitably formulated additives has improved resistance to stress cracking in air, and also in contact with media which give rise to stress cracking.
The polymer composition of the invention comprises at least one cycloolefin copolymer prepared by polymerizing from 0.1 to 99.9% by weight, based on the total amount of monomers, of at least one polycyclic olefin of the formula I, II, IIxe2x80x2, III, IV, or V 
where R1 to R8 are identical or different and are hydrogen or a hydrocarbon radical, and the meaning of the same radical may change in the different formulae, and from 0 to 99.9% by weight, based on the total amount of monomers, of at least one monocyclic olefin of the formula VI 
where n is a number from 2 to 10, and from 0.1 to 99.9% by weight, based on the total amount of monomers, of at least one acyclic 1-olefin of the formula VII 
where R9 to R12 are identical or different and are hydrogen or a hydrocarbon radical, preferably a C6-C10-aryl radical or a C1-C8-alkyl radical.
Preference is given to cycloolefins of the formula I or III, where R1 to R8 are identical or different and are hydrogen or a hydrocarbon radical, in particular a C6-C10-aryl radical or a C1-C8-alkyl radical, and the meanings of identical radicals may change in the different formulae.
Where appropriate, one or more monocyclic olefins of the formula VI are used for the polymerization.
Preference is also given to an acyclic olefin of the formula VII, where R9 to R12 are identical or different and are hydrogen or a hydrocarbon radical, preferably a C6-C10-aryl radical or C1-C8-alkyl radical, such as ethylene or propylene.
Copolymers are in particular prepared from polycyclic olefins, preferably of the formulae I and III, with ethylene.
Particularly preferred polycyclic olefins are norbornene and tetracyclo-dodecene, and these may have C1-C6-alkyl substitution. They are preferably copolymerized with ethylene. Very particular preference is given to ethylene-norbornene copolymers and ethylene-tetracyclododecene copolymers.
The cycloolefin polymers are prepared by heterogeneous or homogeneous catalysis using organometallic compounds. Catalyst systems based on mixed catalysts made from titanium salts and from aluminum organyl compounds are described in DD-A-109 224 and DD-A-237 070. EP-A-156 464 describes the preparation using vanadium-based catalysts. EP-A-283 164, EP-A407 870, EP-A-485 893 and EP-A-503 422 describe the preparation of cycloolefin polymers using catalysts based on soluble metallocene complexes. The preparation processes described in these patents for preparing cycloolefin copolymers, and the catalyst systems used, are expressly incorporated herein by way of reference.